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Neonicotinoids in Groundwater: Presence and Fate in Two Distinct Hydrogeologic Settings in Ontario, Canada

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Title: Neonicotinoids in Groundwater: Presence and Fate in Two Distinct Hydrogeologic Settings in Ontario, Canada
Author: Browne, David Chalker
Department: School of Engineering
Program: Engineering
Advisor: Levison, Jana
Abstract: Neonicotinoids are a group of insecticides that are commonly used in agriculture throughout the world. Despite their widespread use, there are significant knowledge gaps related to the presence and fate of neonicotinoids in groundwater. This research consists of a seasonal groundwater sampling regime, soil sampling, a crop survey, and mathematical modelling exercises which aim to test the environmental parameters governing the transport of clothianidin, imidacloprid, and thiamethoxam to groundwater in two distinct hydrogeologic settings. Both of these research sites are located in Ontario, Canada: one comprises an unconfined, sandy quaternary aquifer while the other consists of a fractured, crystalline bedrock aquifer (Canadian Shield) under a thin layer of overburden. Groundwater sampling was conducted using between 18 and 26 monitoring intervals at each research site in April 2016, July 2016, August 2016, November 2016, and April 2017. All laboratory analysis was conducted using the LC ESI(+) MS/MS at the University of Guelph Ridgetown Campus. Results from groundwater sampling found the neonicotinoids clothianidin, imidacloprid, and thiamethoxam with maximum concentrations and detection frequencies above the level of quantitation of 2.09 µg/L, 0.7 µg/L, 0.46 µg/L, and 2.2%, 0.9%, 1.3%, respectively. Clothianidin peaked at four monitoring intervals in August 2016 (approximately three months after seed sowing and two months prior to harvesting). Imidacloprid was found at low concentrations that were marginally above the level of quantitation during July and August sampling. Thiamethoxam was found at one monitoring interval in Lanark County during both spring freshet (April) sampling rounds. Mathematical modelling revealed that under similar environmental conditions, clothianidin and thiamethoxam are released in a similar pattern that resembles a pulse. The delayed release of thiamethoxam to one monitoring interval in Lanark County was likely due to unusually low permeability overburden near the well. In both of these hydrogeologic settings, modelling revealed that the transport of both clothianidin and thiamethoxam is dominated by processes in the vadose zone. Future research into this subject should focus on how neonicotinoids behave within different climatic and hydrogeologic settings outside of Ontario, Canada.
Date: 2017-09
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